The present invention relates to a bisphenol-phosphorus compound complex and a thermally processed image recording material containing it.
As thermally processed image recording materials, there are a photothermographic material that has a photosensitive layer comprising a catalytically active amount of photocatalyst (e.g., silver halides), a heat developing agent, a reducible silver salt (e.g., silver salts of an organic acid), and a toning agent for controlling silver color tone as required, which are dispersed in a binder matrix, and a thermally processed image forming material that has a photosensitive layer comprising a heat developing agent, a reducible silver salt (e.g., silver salts of an organic acid), and a toning agent for controlling silver color tone as required, which are dispersed in a binder matrix. The thermally processed image forming material is heated imagewise at a high temperature to form monochromatic silver images through an oxidation-reduction reaction between the reducible silver salt (which functions as an oxidizing agent) and the heat developing agent. The photothermographic material is heated at a high temperature after imagewise light exposure to form monochromatic silver images through an oxidation-reduction reaction between the silver halide or the reducible silver salt (which functions as an oxidizing agent) and the heat developing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image of silver halide generated upon exposure. Therefore, the monochromatic silver images are formed in exposed areas of the material. These materials are disclosed in many references including U.S. Pat. No. 2,910,377 and Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 43-4924.
Since the aforementioned thermally processed image recording materials are not subjected to a fixation treatment after the heat development, they suffer from a problem that the thermally reactive silver salt of an organic acid and reducing agent are left as they are in the thermally processed image recording materials, and thus white portions are colored when the materials are stored for a long period of time after the development. o-Bisphenol type reducing agents are frequently used for the thermally processed image recording materials, since they show high reactivity. If their amounts are reduced, the coloration of white portions can be effectively suppressed. However, if the amounts of the o-bisphenol type reducing agents are reduced, sufficient image density can no longer be obtained. Therefore, it is difficult to compromise the image storability and the image density.
Therefore, an object of the present invention is to provide a thermally processed image recording material that can provide sufficient image density at a practical reaction temperature (specifically 100-140xc2x0 C.) and within a practical reaction time (specifically 1-30 seconds), and can sufficiently suppress the coloration of white portions when the material is stored in a dark place after the development. Further, another object of the present invention is to provide a compound useful as a reducing agent that can reconcile the image density and the image storability.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found a surprising effect that if a complex obtained from a bisphenol compound, which is known as a reducing agent used for thermally processed image recording materials (see, for example, European Patent Publication EP0803764A1, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 51-51933, JP-A-6-3793 etc.), and a phosphorus compound is used, sufficient image density could be obtained and the image storability was markedly improved without substantially decreasing the reducing property. Thus, the present invention was accomplished.
That is, the present invention provides bisphenol-phosphorus compound complexes represented by the following general formula (1): 
In the general formula (1) R1, R2, R3 and R4 each independently represent hydrogen atom or a group that can be a substituent on a benzene ring, and L represents xe2x80x94Sxe2x80x94 group or a xe2x80x94CHR5xe2x80x94 group. R5 represents hydrogen atom or an alkyl group. R6, R7 and R8 each independently represent an alkyl group, an aryl group, a heterocyclic group, xe2x80x94N(R9)(R10) or xe2x80x94O(R9). R9 and R10 each independently represent an alkyl group, an aryl group or a heterocyclic group. Two or more groups selected from R6, R7, R8, R9 and R10 may be bound together to form a ring.
Preferred bisphenol-phosphorus compound complexes of the aforementioned general formula (1) are those wherein R1, R2, R3 and R4 each independently represent an alkyl group, L represents a xe2x80x94CHR5xe2x80x94 group, R5 represents hydrogen atom or an alkyl group, R6, R7 and R8 each independently represent an alkyl group, an aryl group or xe2x80x94O(R9), and R9 represents an alkyl group or an aryl group.
The present invention also provides a thermally processed image recording material comprising a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions and a binder on one surface of a support, wherein the thermally processed image recording material comprises at least one kind of the bisphenol-phosphorus compound complex represented by the aforementioned general formula (I). The thermally processed image recording material of the present invention preferably contains at least one kind of photosensitive silver halide.
The thermally processed image recording material of the present invention utilizing the bisphenol-phosphorus compound complex represented by the following general formula (1) can provide sufficient image density at a practical reaction temperature (specifically 100-140xc2x0 C.) and within a practical reaction time (specifically 1-30 seconds), and can sufficiently suppress the coloration of white portions when the material is stored in a dark place after the development.